1. Field of the Invention
The present invention relates to a method for producing an aqueous emulsion of polyurethane (hereinafter referred to as "PU". More precisely, it relates to a method for producing an aqueous PU emulsion having good solvent resistance and water resistance and having good compatibility with other aqueous emulsions to give stable mixtures with them.
2. Description of the Related Art
As a resin for caulking or sealing boundary areas between rubber and plastics, PU has many applications in various fields for coating materials, adhesives, artificial leathers, etc. Recently, aqueous PU has been increasing for meeting the social needs of environmental protection, resources saving, safety, etc. The recent progress in the technique of emulsifying and dispersing PU in water, the technique of self-emulsification and dispersion of PU through ionomerization and the technique of increasing the molecular weight of PU in water has been improving the properties of aqueous PU. In JP-A-53-79990, proposed is the use of a water-soluble salt of a condensate of an acidic amino acid and a fatty acid as the emulsifier for PU.
However, conventional aqueous PU is problematic in that it is often influenced by the emulsifier and others as used in producing it whereby the solvent resistance and water resistance intrinsic to PU is lowered. In addition, when aqueous PU is blended with other various aqueous emulsions, there often occurs another problem of poor compatibility between them.